updates the provides_extras to provides_extra conforming with pypi warehouse

Signed-off-by: javanlacerda <javanlacerda@google.com>

Author: javanlacerda

tests/test_package.py

@@ -177,7 +177,7 @@ def test_metadata_dictionary_keys():
         "requires_external",
         "requires_python",
         # Metadata 2.1
-        "provides_extras",
+        "provides_extra",
         "description_content_type",
         # Metadata 2.2
         "dynamic",
@@ -268,7 +268,7 @@ def test_metadata_dictionary_values(gpg_signature):
     assert result["requires_python"] == meta.requires_python
 
     # Metadata 2.1
-    assert result["provides_extras"] == meta.provides_extras
+    assert result["provides_extra"] == meta.provides_extras
     assert result["description_content_type"] == meta.description_content_type
 
     # Metadata 2.2

twine/package.py

@@ -177,7 +177,7 @@ def metadata_dictionary(self) -> Dict[str, MetadataValue]:
             "requires_external": meta.requires_external,
             "requires_python": meta.requires_python,
             # Metadata 2.1
-            "provides_extras": meta.provides_extras,
+            "provides_extra": meta.provides_extras,
             "description_content_type": meta.description_content_type,
             # Metadata 2.2
             "dynamic": meta.dynamic,